The long-term objective of our research is to understand the mechanisms by which obesity, and specifically upper body obesity, causes insulin resistance and the other health problems such as Type 2 Diabetes. Our focus is on the why the release of free fatty acids (FFA) from adipose tissue lipolysis is abnormal in humans who develop upper body/visceral obesity (UBO) and Type 2 Diabetes (T2DM). The specific aims of this proposal are to: 1) test whether impaired insulin-induced suppression of lipolysis (FFA release) is related to the inflammatory and adipocyte characteristics in groups of individuals known to vary widely with regards to regulation of adipose tissue lipolysis; 2) whether the reductions in adipose tissue inflammation and improvements in adipocyte function that accompany weight loss are predictive of improved insulin-regulation of lipolysis; 3) define if, and so how, the omega-3 fatty acid-induced improvements in adipose inflammatory cell content correlate with reductions in adipose cytokine content and improvements in the insulin IC50 for FFA. We will measure of insulin-regulated adipose tissue lipolysis in vivo and assess adipose tissue inflammation in obese humans with widely varying degrees of insulin resistance before and after weight loss and before and after treatment with omega-3 fatty acids vs. placebo. Omega-3 fatty acids have been shown to reduce adipose tissue macrophage content in humans. Our hypothesis is that the amount and type inflammation predicts adipose insulin resistance; TNF is believed to down regulate perilipin, which would result in under-restrained access of lipases to lipid droplets, whereas IL-6 it believed to impair insulin signaling. We will measure the inflammatory cell content of adipose tissue, including classically activated macrophages and senescent preadipocytes, the tissue content of IL-6 and TNF, readouts of adipocyte TNF and insulin signaling, as well as adipocyte perilipin content. Combined, we believe these studies will offer insights as to why adipose tissue lipolysis is abnormal in some obesity phenotypes and whether therapies directed towards reducing adipose inflammation can improve metabolic health.